Interpretive Summary: Seed dormancy can be a great problem in seed production of sunflower where seeds need to be planted shortly after harvest. Great efforts have been made to develop techniques in breaking seed dormancy of sunflower. Studies have indicated that sunflower genotypes show a large variability in dormancy. In the present study, a large variability was observed among sunflower genotypes and hybrids in the degree of dormancy. In general, sunflower hybrids showed greater levels of seed dormancy than the cultivated genotypes. Some genotypes are highly dormant, and some are nearly non-dormant. The non-dormant lines could be use in breeding programs to reduce dormancy in hybrid sunflower. Techniques using various chemicals have been developed that give reasonable results, but are not simple and are very expensive for farmers in developing countries. The use of 15 h or 20 h priming period is considered very simple and inexpensive to break seed dormancy and can be handled by most farmers. In addition the priming may improve seedling vigour. It is assumed that the priming could have made some biochemical changes in the seed leading to the breaking of seed dormancy and enhancing seed germination and vigour in sunflower.

Technical Abstract:
Seed dormancy is a draw back that causes a great problem in efficient seed production of sunflower for which great efforts have been made to develop techniques in breaking seed dormancy of sunflower. Studies have indicated that sunflower genotypes show a large variability in dormancy. A few nearly non-dormant genotypes have been identified which may be incorporated into breeding programs for this trait. Different periods of hydro-priming (15 and 20 h) were tested to determine their effects in breaking dormancy. Priming for 15 h improved germination percentage and had higher seedling vigour than the 20 h priming period. This priming period is considered a novel technique to break dormancy and to improve seedling vigour in sunflower. Priming for a 15 h period showed a significant increase in germination percentage compared to the control. In another study, the same sunflower hybrid obtained from different sources showed variability in dormancy, where a 15 h priming period improved germination significantly in most of the sources except for a few. This indicates that prevailing climatic conditions in different regions have great impact on seed dormancy in sunflower. It is assumed that the priming could have made some biochemical changes in the seed leading to the breaking of seed dormancy and enhancing seed germination and vigour in sunflower.